This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 00117208.9 filed in Europe on Aug. 11, 2000; the entire content of which is hereby incorporated by reference.
The invention relates to a process and apparatus for the colorimetric measurement of a two-dimensional original. More particularly, the invention relates to a process wherein a color measuring head is moved two-dimensionally relative to the original for the measurement of the original at preselected measuring positions.
The wide-spread distribution of color-enabled computer peripherals and the generally higher quality requirements regarding the orthochromaticity of printed products, the so-called color management, which means the mutual co-ordination of all color-enabled computer peripheral apparatus (monitor, scanner, printer, etc.) as well as the colorimetric control of output apparatus, are of ever increasing importance.
The generation of manufacturer-specific or norm-specific (for example ITC) apparatus profiles is a central point of the color management. These apparatus profiles enable the conversion of apparatus specific color values into apparatus independent, and therefore commonly valid and transmittable color values. The generation of apparatus profiles is based on the characterization of the colorimetric properties of the input and output apparatus such as color printers and scanners. This requires the colorimetric evaluation of color test cards (so called test charts) as described, for example, in the ISO norm IT8. Such a test chart is commonly composed of several hundred test fields.
A number of methods exist today for the measurement of the color fields of a test chart.
For example, the color fields are individually measured by way of a handheld color measuring apparatus, which means a colorimeter or spectrometer as described, for example, in U.S. Pat. No. 5,684,582, the disclosure of which is hereby incorporated by reference in its entirety, which represents a significant amount of work for several hundred measurement fields.
Or the color fields are scanned in with a scanning handheld measuring apparatus, as described, for example, in DE-A 197 16 066, by manually moving the apparatus over the lines of the test chart. Compared to the method with individual manual measurements, the cost is massively reduced. However, the quality of the measuring results depends on the skills of the user because of the manual operation.
An apparatus is known from DE 197 22 073, the disclosure of which is hereby incorporated by reference in its entirety, wherein a line printer is reconfigured in such a way that it can capture color measurement data from fields found on the printout either simultaneously with the printing process or thereafter with an integrated color measuring head. This process has several disadvantages. If one measures after the printing, the original is not dry and the color measurement data can still change after the measurement. If one measures after the printing, the paper must be newly fed in, which can create problems during the positioning of the color measuring head on the original. Furthermore, a line printer can normally not be equipped with an illumination for transmission measurements because of space constraints. In addition, because of the non-linear path of the original through the printer, only flexible originals can be measured. The evaluation of, for example, a relatively stiff printed cardboard of a packaging is not possible. Scanning measuring apparatus determines the position of the color fields from the analysis of the measured values and therefore pose special requirements on the positioning of the color fields. The color fields must be so large or the apparatus must be moved so slowly that at least two complete measurements per field can be achieved.
U.S. Pat. No. 5,369,494, the disclosure of which is hereby incorporated by reference in its entirety, describes a measuring apparatus which can pull in an original inserted by the user and measure it strip by strip. The user must feed in the original once for each color field row of the test chart. This manual feeding creates work for the user and leaves room for manipulation errors. Strip by strip measuring apparatus work by scanning and therefore pose the above described requirements for the positioning and dimensioning of the color fields.
A further known process includes the use of a measuring apparatus mounted on an X Y displacement table which measures the test chart under the control of a computer. A typical representative of such an arrangement is the combination of applicant""s apparatus sold under the names Spectralino and SpectroScan. At the beginning of the measurement process, the user must supply to the apparatus the position of the corner points of the measurement field arrangements, which represents a potential source for errors.
An apparatus is know from EP 0 847 187, the disclosure of which is incorporated by reference in its entirety, which can spectrally capture the image information of a complete printed sheet, in that a measuring bar with many measuring heads arranged in a row is moved over the original. Such an apparatus can be described as spectral scanner. With such a special scanner, a maximum of information can be quickly obtained from an original. However, such an apparatus can only be realized with high technical and financial cost, has a large space requirement, and has a low local resolution.
It is now an object of the invention to improve a process and apparatus of the generic type in such a way that the constructive and conceptional pre-requisites are created to carry out, within a short time and at an acceptable constructive cost, the complete procedure of the measuring in of a remitting or transmitting original without interaction of the user, whereby the amount of work of the user is reduced to a minimum and manipulation errors are at the same time precluded.
The solution of this object which forms the basis of this invention is achieved in the preferred embodiment in that the original is photoelectrically scanned, the measuring positions are determined from a color representation of the original, and the original is then colorimetrically measured at the measuring positions.
According to the basic aspect of the invention, the image information of the original is on the one hand electronically captured at high resolution and analyzed with image processing methods and the information about the original which is obtained from the analysis is then used on the other hand to control the positioning of the color measuring head. The color measuring head thereby provides for the capturing of colorimetric values at the measuring positions of the original for the respective application.
The range of applications of the invention includes, for example, the capturing of the colorimetric values of the numerous color fields of a test chart, which can be used for the generation of ICC profiles, for the control of color-enabled output devices directly from the measured colorimetric values of the original, which are typically an image. The complete process of measuring in of a remitting or transmitting test chart can be carried out without the interaction of the user and within a short time. The amount of work for the user is thereby reduced to a minimum and manipulation errors can be precluded.
Depending on the respective type of the apparatus of the invention, it can also be used as a self calibrating and self profiling and thereby color binding digital camera or scanner.